Helicobacter pylori has been shown to cause chronic active gastritis and peptic ulcer disease, and it is associated with the development of gastric adenocarcinoma, the fourth most common cancer in the world. Additionally, there is a suggestion that in the developing world, infection with H. pylori in childhood increases the likelihood of developing chronic diarrhea, malnutrition, and growth failure. It is estimated that the yearly world medical cost to treat H. pylori gastritis and peptic ulcer alone exceeds $7.4 billion. In parts of the developing world, up to 90% of the population is infected with H. pylori by ten years of age. The exact mode of transmission and the risk factors associated with the acquisition of an H. pylori infection are largely unknown, especially in the developing world. In this study, Branch investigators plan to describe the epidemiology of H. pylori infection in a population-based cohort of rural Egyptian children followed from birth until three years of age. The database from this cohort will include baseline sociodemographic features, periodic monitoring of diet and anthropometric status, systematic monitoring for ascertainment of etiologically defined diarrheal illnesses, and systematic monitoring for ascertainment of prevalent and incident H. pylori infections. With these data, age-specific incidence rates for H. pylori infection will be calculated. In addition, Branch investigators will relate the occurrence of prevalent and incident H. pylori to antecedent sociodemographic, hygienic, behavioral, and dietary characteristics, and to levels of IgA anti-H. pylori antibodies in breastmilk ingested by breast-feeding infants. Finally, the rates of persistent diarrhea, and the risks of wasting and stunting will be assessed. To date 200 neonates have been enrolled into the study, the first of whom was enrolled on 2/1/98.